The ascending flue is a passage connecting the sedimentation tank and the waste heat boiler, and is used to discharge the furnace gas into the waste heat boiler. It is necessary to prevent the rising flue from being blocked by the melt adhesion and to minimize the radiant heat loss of the sedimentation tank.

The shape of the rising flue is of a vertical type and a tilt type. In order to avoid flue nodulation, most flash furnaces use inclined ascending flue, and the cross-sectional area at the junction with the waste heat boiler is generally 8 to 8.5 m.

Design, large flash furnaces can be appropriately increased. The ascending flue is the same as the sedimentation tank. The brick is built in the steel plate and the top is suspended. The ascending flue is provided with an accidental heavy oil nozzle to remove the adhesive from the connection between the flue and the waste heat boiler. Production practice has shown that with oxygen-enriched air containing 25% oxygen, the melting rate of the furnace is twice that of ordinary air.

A slag curtain is installed at the junction of the ascending flue and the waste heat boiler, and its function is as follows.

1 Reduce the amount of soot entering the waste heat boiler, and reduce the amount of soot that accounts for 1%~2% of the charge. Especially for the dust containing lead and zinc, after sticking to the slag curtain, it is melted and dropped into the flash furnace by burning oil and burning oxygen.

2 Reduce the cleaning of waste heat boilers and increase their thermal efficiency.

3 Prevent the radiant heat of the flash furnace from entering the waste heat boiler to ensure stable operation of the boiler.

The slag curtain is composed of a plurality of layers of separate U-shaped water pipes, and may be composed of one or two or three layers of slag curtains of different thicknesses as needed. Cooling water is passed through the water pipe, and the pipe surface is coated with refractory material. The inlet water temperature is 303K, the outlet water temperature is 323K, and each pipe is easy to handle.

The semi-fused soot and metal vapor carried out from the furnace gas are cooled and condensed, and adhered to the pipe wall to form a slag curtain. In order to prevent the slag curtain from being too thick and blocking the passage, the thickness of the slag layer must be adjusted. To this end, a burning oil or an oxygen burning device is arranged near the slag curtain, and the excessively thick slag layer is burned by burning oil or burning oxygen; at the same time, the cooling water temperature is adjusted to control the thickness of the slag layer.